1. Field of the Invention
This invention relates in general to subsea wellheads, and in particular to a running tool for installing load shoulders in the wellhead.
2. Description of the Prior Art
When drilling a well for oil or gas, typically a wellhead housing will be mounted at the upper end of the well to a large diameter string of conductor pipe. The well is then drilled deeper and a string of casing will be run. Subsequently, the well will be drilled to a greater depth and at least one more string of casing will be installed.
A casing hanger is located at the upper end of each string of casing, the casing hanger landing on a load shoulder in the wellhead housing. In one type of wellhead housing, the shoulders are machined into the bore of the wellhead housing. In another type, the load shoulders are separate high strength rings that are installed into grooves in the wellhead housing while the wellhead housing is being manufactured. In both cases, the inner diameter of the wellhead housing bore will decrease in a downward direction, with the smallest inner diameter located below the lower shoulder.
The stepped diameter bore has a disadvantage. Drilling tools can be no larger than the minimum inner diameter located below the lower shoulder. Sometimes, it is desired to utilize a drill bit or tool that is larger than minimum inner diameter. U.S. Pat. No. 4,886,121 shows a load ring installed with a running tool after the wellhead housing is in place. In that patent, it is necessary to install a pin from the exterior of the wellhead. The pin extends through the wellhead housing below each groove for engagement by the load shoulder during the running process. The pin has to be screwed in to extend it from a full bore position to a position protruding into the bore. This presents a drawback for subsea wells, as it will require a diver or remote operated vehicle to rotate the pins from the subsea environment. Also, providing sealed threaded holes and threaded pins would be expensive.